U.S. patent number 4,678,999 [Application Number 06/675,174] was granted by the patent office on 1987-07-07 for charge depletion meter.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Air. Invention is credited to Josef F. Schneider.
United States Patent |
4,678,999 |
Schneider |
July 7, 1987 |
Charge depletion meter
Abstract
A charge depletion meter apparatus having a current to frequency
converter to sense and convert the current drain of a battery
source to a digital signal which is divided and then accumulated in
a counter. An LCD display unit displays the accumulated charge
which is received from the counter.
Inventors: |
Schneider; Josef F.
(Albuquerque, NM) |
Assignee: |
The United States of America as
represented by the Secretary of the Air (Washington,
DC)
|
Family
ID: |
24709356 |
Appl.
No.: |
06/675,174 |
Filed: |
November 27, 1984 |
Current U.S.
Class: |
324/427; 320/149;
340/636.13; 340/636.15 |
Current CPC
Class: |
G01R
31/36 (20130101) |
Current International
Class: |
G01R
31/36 (20060101); G01N 027/46 () |
Field of
Search: |
;324/427,426,428
;320/48,48X ;340/636 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Mueller; Robert W.
Attorney, Agent or Firm: Stepanishen; William Singer; Donald
J.
Government Interests
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or
for the Government for governmental purposes without the payment of
any royalty thereon.
Claims
What is claimed is:
1. A charge depletion meter apparatus comprising in
combination:
a sensing means connected to a battery source to sense the amount
of charge flowing therethrough, said sensing means providing a
charge signal,
a current to frequency converter means coupled to said sensing
means to receive said charge signal therefrom, said current to
frequency converter means converting said charge signal to a
digital signal which is representative thereof,
a divider means coupled to said current to frequency converter
means to receive said digital signal therefrom, said divider means
dividing said digital signal by a predetermined number, said
divider means providing an output pulse signal,
a decimal counter means coupled to said divider means to receive
said output pulse signal, said decimal counter means accumulating
said output pulse signal,
reset means coupled respectively to said divider means and said
decimal counter means for manually resetting both to zero, and,
a display means coupled to said decimal counter means to receive
said output pulse signal therefrom, said display means displaying
said output pulse signal.
2. A charge depletion meter apparatus as described in claim 1
wherein said sensing means comprises a resistor.
3. A charge depletion meter apparatus as described in claim 2
wherein said predetermined number equals 409,600 to 1.
4. A charge depletion meter apparatus as described in claim 3
wherein said divider means comprises a first divider unit with a
first predetermined division factor, and,
a pair of second divider units in series with each other with a
second predetermined division factor, said pair of second divider
units connected in series with said first divider unit.
5. A charge depletion meter apparatus as described in claim 4
wherein said display means comprises a 41/2 digit LCD display
unit.
6. A charge depletion meter apparatus as described in claim 4
wherein said first predetermined division factor equals 2.sup.14 to
1 and said second predetermined division factor equals 5 to 1.
Description
BACKGROUND OF THE INVENTION
The present invention relates broadly to battery capacity
measurement apparatus and in particular to a charge depletion
meter.
In the prior art one of the more reliable methods of determining
the state of charge of lead-acid battery was the hydrometer test.
Sulphuric acid which is commonly used in a lead-acid battery is
heavier than water. Therefore, the mixture of sulphuric acid and
water which is used as the electrolyte, is heavier than pure water
and its specific gravity may be measured.
When a battery is fully charged, the electrolyte has a specific
gravity reading of about 1.250 to 1.290. This reading means that
the given amount of the electrolyte in the battery will weigh 1.25
to 1.29 times as much as the same volume of pure water. As the
battery discharges, some of the heavier sulphuric acid is broken up
and unites with the battery plates to form a lead sulphate coating
on the plates. The remaining electrolyte, therefore, becomes
lighter and lighter as the battery discharges. For this reason, it
is possible to tell how much a battery has become discharged simply
by measuring the specific gravity of the electrolyte.
The instrument which is used to measure the specific gravity of the
electrolyte in a battery is the hydrometer. The hydrometer consists
of a glass barrel with a small float inside. A hydrometer reading
is taken by squeezing the rubber bulb at the top, inserting the
hard rubber nozzle into one cell of the battery, and releasing the
bulb to draw some of the electrolyte up into the barrel. When the
electrolyte has risen to a convenient level for accurate reading,
it is prevented from rising farther by a small tube. This method of
measuring the state of charge of a battery is strictly manually and
time-consuming. The present invention provides a completely
automatic charge monitoring and measuring apparatus.
The charge depletion meter apparatus solves the problem of knowing
exactly how much charge has been drained from a battery at any one
time. Consequently, it is known how much charge is left in it and
battery replacement can be handled on a more economic basis.
Therefore, the charge depletion meter solves the problem of keeping
track of consumption when a battery is frequently turned on and off
or when widely varying loads are encountered.
SUMMARY OF THE INVENTION
The present invention utilizes a current to frequency converter
unit to measure the current being drawn from a battery. The
converter output is divided by a scale factor to display the
battery charge consumption in one of three ampere-hour ranges in a
continuous, digital decimal display.
It is one object of the present invention, therefore, to provide an
improved charge depletion meter apparatus.
It is another object of the invention to provide an improved charge
depletion meter apparatus which is a completely solid state
ampere-hour measuring device configured to show in a continuous,
digital decimal display the accumulated charge used by a device or
taken from a source.
It is another object of the invention to provide an improved charge
depletion meter apparatus which uses a current to frequency
converter unit to measure the charge consumption by means of
frequency dividers that provide total accumulation for display in a
display counter.
It is another object of the invention to provide an improved charge
depletion meter apparatus wherein even the minutest charge
consumption is accumulated until a resolution unit is reached and
displayed.
It is another object of the invention to provide an improved charge
depletion meter apparatus wherein the converter and the divider
units are remote to one another and are connected by a transmission
line.
These and other advantages, objects and features of the invention
will become more apparent after considering the following
description taken in conjunction with the illustrative embodiment
in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram, partially in schematic, of the charge
depletion meter apparatus in its test configuration,
FIG. 2 is a block diagram of the charge depletion meter apparatus
according to the present invention, and,
FIG. 3 is a circuit diagram showing in greater detail the charge
depletion meter apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1 there is shown a charge depletion meter
apparatus 10 connected to a battery source 12. A current sensing
resistor 14 is connected in series with the battery source 12 and
is connected across the input to the charge depletion meter
apparatus 10. The charge depletion meter apparatus 10 derives its
power for operation from the battery source 12. A display unit 16
is connected to the charge depletion meter apparatus 10 to display
the charge use and state of the battery source 12.
The charge depletion meter is a completely solid state ampere-hour
measuring device which is configured to show in a continuous,
digital decimal display the accumulated charge used by a device or
taken from a source. It is calibrated in units of ampere-hours and
has a full scale of 20, 200, and 2000 Ah with a resolution of
0.001, 0.01, and 0.1 Ah, respectively, on a 41/2 digit display.
The current to be measured is sensed by a low ohm resistor (1, 0.1,
0.01 ohm) which provides approximately 1 ma at full scale into a
current-to-frequency converter. This current is adjusted so that
the full scale output of the converter reaches 11,378 pulses per
second, for any full scale of 0.1, 1, or 10A at the sensing
location.
The converter output is divided by a factor of 409,600 to advance
the display by the resolution unit of 0.001, 0.01, 0.1 Ah every
1/100 of an hour at full scale. The divider chain and the 41/2
digit display counter can be reset to zero by means of a reset
button. The use of CMOS circuitry assures low power consumption and
operation over a 5 to 7 volt supply variation.
The charge depletion meter apparatus operates on a full scale
reading of 1 A. The sensing resistor is inserted in the
battery-common connection. The charge depletion meter apparatus
(CDM) measures the current which is provided by this voltage drop
and is powered by the same battery at a tiepoint if necessary to
obtain proper voltage.
Turning now to FIG. 2, there is shown a block diagram of the charge
depletion meter apparatus wherein the current to frequency
converter unit 20 is utilized to measure the current drain of a
battery source under test (not shown). First and second
potentiometers P.sub.1 +P.sub.2 are provided to permit full scale
and linearity adjustment of the current to frequency converter unit
20. The analog input signal to the current to frequency converter
unit 20 is converted to a digital signal which is applied to the
divider unit 22. The divider unit 22 divides down the digital
signal by a predetermined number, such as 409,600 to 1. The output
of the divider unit 22 is applied to the 41/2 digit counter unit 24
wherein the output pulses are accumulated. The results of the 41/2
digit counter unit 24 are displayed in display unit 28. A reset
means 26 is coupled to both the divider unit 22 and the 41/2 digit
counter unit 24 to permit the manual resetting of both units.
There is shown in FIG. 3 a circuit diagram of the charge depletion
meter wherein the current to frequency converter unit 30 comprises
the integrated circuit AD537. The divider unit 32 which receives
the digital signal from the current to frequency converter unit 30,
comprises three integrated circuits, CD 4020 and two MC 74C90 units
respectively. The 41/2 digit counter unit 34 which accumulates the
charge signal, comprises an integrated circuit counter ICM 7224.
The display unit 36 comprises an LCD display unit LCD 5675. A reset
button 38 is connected to permit both the divider unit 32 and the
41/2 digit counter unit 34 to be reset respectively both units to
zero.
The input current is adjusted with potentiometer P1 to yield a
frequency output 11,378 pulses per second, which represents the
full-scale output of the converter unit 30 for a 100 mV drop on the
sensing resistor. Linearity is adjusted with potentiometer P2 by
correcting the offset of the converter unit 30. Capacitor C1 sets
the basic frequency of the converter 30. The output pulses are
divided first by a compact 16,384:1 divider (CD 4020) and then by
two consecutive 5:1 dividers (MC 74C90) to yield a total division
factor of 409,600:1.
The divider output pulses are accumulated in a 41/2 digit decimal
counter unit 34 in units of 0.001, 0.01, 0.1 Ah respective to the
use of a 1, 0.1, 0.01.OMEGA. sensing resistor. Charge depletion
amounts which are below the resolution unit of the counter are
still accumulated in the divider and therefore there is no
threshold barrier. The LCD display unit 36 is driven by the counter
module 34, which provides the LCD backplane frequency (BP). It is
set to about 30 Hz by capacitor C2. The supply voltage (VCC)
dropping resistors R3, R4, R5 decouple the individual integrated
circuit units and provide proper operating range. A reset button 38
forces the divider and the counter to zero. The components of the
divider and the counter are of the CMOS type with a total supply
current of approximately 150 .mu.A. The converter needs a supply
current of approximately 1.5 ma. While the converter unit 30 can be
turned off when the load is removed, the divider unit 32 and the
counter unit 34 should stay on the battery all the time, thereby
holding the accumulated measurement. The constant drain of 150
.mu.A produces a count (=resolution unit) every 2.8 days. Even
after four weeks, only 0.1 Ah have accumulated which is 0.05%
referred to the display capacity of 200 Ah. If this cannot be
tolerated, a CMOS oscillator can be switched in, in lieu of the
converter unit to produce 1.7 pulses per second at the divider
input, the equivalent of the converter output for 150 .mu.A in
order to keep the count accurate.
Further uses and modifications that are envisioned are:
a. the counter be counted down which would show the charge still
left in a battery when started at the batteries' capacity;
b. the counter be counted up as well as down which could be used to
measure both discharge and charge of a rechargable battery;
c. a low battery indicator be derived from a count comparison with
a value preset for a particular battery;
d. the display be done in LED when power consumption is of no
consequence;
e. the divider and the counterparts use non-volatile
technology;
f. the meter be calibrated to read percent of full charge
capacity;
g. a blinking colon or any other symbol in the display indicate
that the meter is working;
h. the divider and counter have their own battery for operation and
for continuous holding of the accumulated count;
i. the readout, especially with LED be normally turned off and only
activated when needed;
j. the meter be used as a regular Ah-meter for all kind of
circuits;
k. the meter be fitted with a rectifier to be used on AC power.
Although the invention has been described with reference to a
particular embodiment, it will be understood to those skilled in
the art that the invention is capable of a variety of alternative
embodiments within the spirit and scope of the appended claims
* * * * *